Light emitting diodes (LEDs) are an important class of solid-state devices that convert electric energy to light. Improvements in these devices have resulted in their use in light fixtures designed to replace conventional incandescent and fluorescent light sources. The LEDs have significantly longer lifetimes than both incandescent bulbs and fluorescent tubes. In addition, the efficiency of conversion of electricity to light has now reached the same levels as obtained in fluorescent light fixtures. Finally, since LEDs operate at relatively low voltages, issues related to the high voltages at which fluorescent light fixtures operate are substantially reduced.
The electrical conversion efficiency and lifetime of LEDs depend on the operating temperature of the LEDs. Increases in temperature lead to a loss in conversion efficiency and a lowering of the LED lifetime. Transferring the heat from the LEDs to the surrounding air is, hence, an important consideration in replacing existing high power lighting systems with LED-based light sources. Typically, LED light sources in the power range of existing fluorescent tube light sources or incandescent based light fixtures require a large heat transfer surface. The heat transfer is typically accomplished by mounting the LEDs on the front side of a carrier that has a heat-conducting bottom surface that is attached to a larger heat-radiating surface in the final light fixture. The design of the final heat-radiating system presents challenges for the light fixture manufacturer.